|Publication number||US7079734 B2|
|Application number||US 11/020,778|
|Publication date||Jul 18, 2006|
|Filing date||Dec 22, 2004|
|Priority date||Dec 22, 2004|
|Also published as||US20060133748|
|Publication number||020778, 11020778, US 7079734 B2, US 7079734B2, US-B2-7079734, US7079734 B2, US7079734B2|
|Inventors||David A. Seddon, William C. Hurley|
|Original Assignee||Corning Cable Systems Llc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (34), Non-Patent Citations (1), Referenced by (20), Classifications (6), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to fiber optic drop cables. More specifically, the invention relates to fiber optic drop cables suitable for outdoor applications such as fiber to the subscriber applications.
Communication networks are used to transport a variety of signals such as voice, video, data transmission, and the like. Traditional communication networks use copper wires in cables for transporting information and data. However, copper cables have drawbacks because they are large, heavy, and can only transmit a relatively limited amount of data. Consequently, optical waveguide cables replaced most of the copper cables in long-haul communication network links, thereby providing greater bandwidth capacity for long-haul links. However, most communication networks use copper cables for distribution and/or drop links on the subscriber side of the central office. In other words, subscribers have a limited amount of available bandwidth due to the constraints of copper cables in the communication network. Stated another way, the copper cables are a bottleneck that inhibit the subscriber from utilizing the relatively high-bandwidth capacity of the long-haul links.
As optical waveguides are deployed deeper into communication networks, subscribers will have access to increased bandwidth. But there are certain obstacles that make it challenging and/or expensive to route optical waveguides/optical cables deeper into the communication network, i.e., closer to the subscriber. For instance, laying the last mile of fiber to the subscriber requires a low-cost fiber optic cable that is craft-friendly for installation, connectorization, slack storage, and versatility. Moreover, the reliability and robustness of the fiber optic cable must withstand the rigors of an outdoor environment.
Conventional outdoor cables use rigid strength elements having relatively large diameters for carrying tensile loads and inhibiting shrinkage of the cable such as a steel or a glass reinforced plastic rod. However, these relatively large rigid strength members make the cable very stiff and relatively large, but the cable designs preserve optical performance in the outdoor environment. In other words, the conventional outdoor cables were designed to be stiff and inhibit bending, thereby protecting the optical fibers therein. However, these conventional outdoor cables dramatically increased the bending radius of the cable and when coiled the strength members act like a coiled spring that wants to unwind. Consequently, these conventional outdoor cables are difficult for the craft to handle in the field and as well as being difficult to work with in factory because the rigid strength members.
Cables have used other strength members such as conventional fiberglass yarns, but they require a relatively large number of conventional yarns and provide little or no anti-buckling strength compared with rigid strength members. Additionally, these types of cable may not withstand the rigors of the outdoor environment with the desired level of reliability. Moreover, the use of a relatively large number of conventional fiberglass yarns increases the manufacturing complexity along with cost of the cable. Thus, the prior art cables do not meet all of the requirements for a drop cable that is suitable for routing optical waveguides to the subscriber.
Using first and second strength assemblies 26,28 are advantageous because besides providing the necessary tensile strength for the fiber optic cables, they allow for greater cable flexibility while still providing the necessary anti-buckling characteristics required for outdoor applications. Cable flexibility is desired in cables intended for subscriber applications because, for instance, it allows for coiling and storing excess cable length and makes the cable easier to route and work with for both the craftsman and factory personnel. In cable 20, strength assemblies 26,28 are generally disposed on opposite sides of buffer tube 24, thereby imparting a preferential bend characteristic to the cable. Additionally, strength assemblies 26,28 are arranged so that the respective plurality of strength members 26 b,28 b are radially disposed about at least half of a circumference of the respective strength components 26 a,28 a. In other embodiments, the plurality of strength members are arranged so that they are radially disposed about the majority, if not the entire, circumference of the strength member.
Strength components 26 a,28 a of respective strength assemblies 26,28 provide fiber optic cable 20 with the majority of its anti-buckling strength along with other characteristic that preserve optical performance. In other words, strength components 26 a,28 a generally resist the shrinking of cable jacket 29 during temperature variations, generally inhibit bending of the cable, and provide tensile strength. However, strength components 26 a,28 a are not intended to carry the entire tensile load of the cable and are selected to allow a desired degree of bending, thereby making the cable suitable for subscriber applications where the appropriate flexibility is required. Strength components 26 a,28 a preferably are dielectric rods of an all dielectric fiber optic cable design. By way of example, strength components are glass-reinforced plastic (grp) rods having a diameter of about 1 mm or less, but other suitable strength component materials, shapes, and/or sizes are possible. For instance, other suitable materials for strength components include conductive wires such as steel and copper.
Strength members 26 b,28 b of respective strength assemblies 26,28 provide tensile strength to fiber optic cable 20 while still allowing flexibility since the strength members are rovings that generally speaking lack anti-buckling characteristics. In other words, strength members 26 b,28 b generally provide tensile strength while allowing bending of the cable. Consequently, fiber optic cables according to the present invention balance the strength element characteristics of the strength components and strength members, thereby preserving optical performance in the outdoor environment while providing the desired flexibility and handling characteristics for ease of use in subscriber applications. By way of example, the plurality of strength members 26 b,28 b are fiberglass yarns or rovings that at least partially contact the respective strength components. Of course, other suitable strength component materials, shapes, and/or sizes are possible. For instance, other suitable materials for strength members include aramid fibers and other high-strength materials such as ultrahigh molecular weight polyethylene sold under the tradename SPECTRA. In one advantageous embodiment, strength members 26 b,28 b include a matrix material that promotes adhesion to cable jacket 29 such as RPLPE ARAGLASS available from NEPTCO, Inc. of Pawtucket, R.I. In still other embodiments, strength members can include a water-swellable component for blocking the migration of water in the cable.
Optical waveguide 22 is preferably a single-mode optical fiber having a tight-buffer layer (not numbered) formed from a polymer or a UV material; however, other types or configurations of optical fibers can be used. For example, optical fibers 22 can be multi-mode, pure-mode, erbium doped, polarization-maintaining fiber, plastic, other suitable types of light waveguides, and/or combinations thereof. For instance, each optical fiber 22 can include a silica-based core that is operative to transmit light and is surrounded by a silica-based cladding having a lower index of refraction than the core. Additionally, one or more coatings can be applied to optical fiber 25 during manufacture for protecting the cladding. For example, a soft primary coating surrounds the cladding, and a relatively rigid secondary coating surrounds the primary coating. The coating can also include an identifying means such as ink or other suitable indicia for identification and/or an anti-adhesion agent that inhibits the removal of the identifying means. Additionally, optical waveguide 22 can have other configurations such being included in a ribbon or a bundle. Suitable optical fibers are commercially available from Corning Incorporated of Corning, N.Y.
Buffer tube 24 is preferably constructed of a polymeric material and is suitably dimensioned for receiving the optical waveguides therein. However, other suitable materials and shapes can be used for buffer tube 24. Buffer tube 24 of the present invention can also include additives for improving flame-retardance; however, any other suitable additives such as for processing can be used. As depicted in
As depicted, fiber optic cable 20 includes at least one water-swellable component therein for inhibiting the migration of water along the cable. Specifically, fiber optic cable 20 includes at least one, and preferably, a plurality of water-swellable yarns or threads 25 disposed within buffer tube 24, but the use of a water-swellable powder or coating is also possible. Water-swellable yarns 25 can serve the function of water-blocking and also act as a coupling element for the optical waveguide. A degree of coupling of the optical waveguide with a portion of the cable is generally desirable for inhibiting optical waveguide 22 from migrating along the tube or cavity and/or inhibiting the transfer of forces from the optical waveguide to the optical connector. Water-swellable yarns 25 can at least intermittently couple optical waveguide 22 with buffer tube 24. In one embodiment, water-swellable yarns 25 have an excess length compared with optical waveguide 22, thereby aiding with coupling. Coupling of optical waveguide 22 is achievable in other manners using other suitable coupling elements. For instance, tube 24 may include other coupling elements such as a thixotropic material such as a grease or gel, a water-swellable tape, a foam tape with or without a water-blocking characteristic, or other like materials that may couple intermittently or continuously along the optical waveguide.
Cable jacket 29 is preferably constructed from a suitable polymeric material for protecting the cable from the rigors of the outdoor environment. Cable jacket 29 generally surrounds buffer tube 24 housing optical waveguide 22 and strength assemblies 26,28. As depicted, fiber optic cable 20 has a generally flat cross-section, but other suitable cross-section are possible. Moreover, cable jacket 29 can include ripcords embedded therein or other preferential tear portions for aiding the craft in opening the cable for fiber access. Additionally, cable jacket 29 can include a toning lobe (not shown) having a conductive wire embedded therein for locating the cable in buried environments.
Cavity 37 of cable jacket 39 includes tight-buffered optical fiber 22 and a plurality of water-blocking yarns 25. In this embodiment, water-blocking yarns are multi-functional since they inhibit the migration of water and act as a coupling element for optical waveguide 22. Tight-buffered optical fiber should not be confused with optical fiber(s) disposed in a buffer tube. Specifically, buffer tubes typically include one or more optical fibers disposed therein that float in a water-blocking grease or the like. Moreover, buffer tubes typically have a relatively large inner diameter compared with the outer diameter of the optical fiber(s) therein. Whereas, one skilled in the art would understand that a buffered optical fiber such as a tight-buffered fiber typically includes a single optical fiber having a buffer layer with an inner diameter that is generally speaking closely matched to the outer diameter of the optical fiber and coupled thereto.
In this embodiment, cable jacket 39 includes a profile that inhibits the transfer of clamping forces to the portion of the cable about cavity 37 and directs the clamping forces to the strength assemblies. In other words, cable jacket 39 includes a hour-glass shaped cross-section where a maximum thickness, i.e., the hips, occurs adjacent to at least one of the strength assemblies and preferably occurs adjacent to both strength assemblies 26′,28′. Also, the cross-section of cable jacket 39 includes a minimum thickness, i.e., a waist, adjacent to the cavity 37 of cable jacket, thereby inhibiting the transfer of clamping forces to this area and protecting optical fiber 22. Likewise, the concepts of cable jacket cross-section may be applied to cable designs other than tubeless.
The concepts of the present invention also provide flexibility in connectorization process of the fiber optic cable. In other words, a connector can grip the strength members, the strength component, or both the strength members and strength components as desired.
Generally speaking, most of the components of plug connector 50 are formed from a suitable polymer. Preferably, the polymer is a UV stabilized polymer such as ULTEM 2210 available from GE Plastics; however, other suitable materials are possible. For instance, stainless steel or any other suitable metal may be used for various components.
As best shown in
As shown in
Cable clamping portion 56 has two outboard half-pipe passageways 56 a and a central half-pipe passageway 56 b that is generally disposed along longitudinal axis A—A. Half-pipe passageways 56 a and 56 b preferably include at least one rib 56 c for securely clamping optical component 42 and strength components 44 after crimp band 54 is crimped, thereby completing the crimp assembly. Moreover, half-pipe passageways 56 a and 56 b are sized for the strength elements, in this case, strength components of cable 20, but the passageways can be sized for different crimping/cable configurations.
Likewise, half-shell 55 a has a connector assembly clamping portion 57 that is sized for attaching connector assembly 52. Specifically, connector assembly clamping portion 57 has a half-pipe passageway 57 a that opens into and connects central half-pipe passageway 56 b and a partially rectangular passageway 57 b. Half-pipe passageway 57 a is sized for securing spring push 52 d and may include one or more ribs for that purpose. Rectangular passageway 57 b holds a portion of connector body 52 a therein and inhibits the rotation between connector assembly 52 and the crimp assembly.
When fully assembled the crimp assembly fits into shroud 60. Additionally, crimp housing 55 is keyed to direct the insertion of the crimp assembly into shroud 60. In this case, half-shells 55 a include planar surfaces 57 e (
Shroud 60 has a generally cylindrical shape with a first end 60 a and a second end 60 b. Shroud generally protects connector assembly 52 and in preferred embodiments also keys plug connector 50 with a respective mating receptacle (not shown). Moreover, shroud 60 includes a through passageway between first and second ends 60 a and 60 b. As discussed, the passageway of shroud 60 is keyed so that crimp housing 54 is inhibited from rotating when plug connector 50 is assembled. Additionally, the passageway has an internal shoulder (not numbered) that inhibits the crimp assembly from being inserted beyond a predetermined position.
As best shown in
A medial portion of shroud 60 has a groove 62 for seating an O-ring 59. O-ring 59 provides a weatherproof seal between plug connector 50 and the receptacle or protective cap 68. The medial portion also includes a shoulder 60 d that provides a stop for coupling nut 64. Coupling nut 64 has a passageway sized so that it fits over the second end 60 b of shroud 60 and easily rotates about the medial portion of shroud 60. In other words, coupling nut 64 cannot move beyond shoulder 60 d, but coupling nut 64 is able to rotate with respect to shroud 60. Second end 60 b of shroud 60 includes a stepped down portion having a relatively wide groove (not numbered). This stepped down portion and groove are used for securing heat shrink tubing 67. Heat shrink tubing 67 is used for weatherproofing the preconnectorized cable. Specifically, the stepped down portion and groove allow for the attachment of heat shrink tubing 67 to the second end 60 b of shroud 60. The other end of heat shrink tubing 67 is attached to cable jacket 29, thereby inhibiting water from entering plug connector 50.
After the heat shrink tubing 67 is attached, boot 66 is slid over heat shrink tubing 67 and a portion of shroud 60. Boot 66 is preferably formed from a flexible material such as KRAYTON. Heat shrink tubing 67 and boot 66 generally inhibit kinking and provide bending strain relief to the cable near plug connector 50. Boot 66 has a longitudinal passageway (not visible) with a stepped profile therethrough. The first end of the boot passageway is sized to fit over the second end of shroud 60 and heat shrink tubing 67. The first end of the boot passageway has a stepped down portion sized for cable 20 and the heat shrink tubing 67 and acts as stop for indicating that the boot is fully seated. After boot 66 is seated, coupling nut 64 is slid up to shoulder 60 c so that wire assembly 69 can be secured to boot 66. Specifically, a first end of wire assembly 69 is positioned about groove 66 a on boot 66 and wire 69 a is secured thereto using a first wire crimp (not numbered). Thus, coupling nut 64 is captured between shoulder 60 c of shroud 60 and wire assembly 69 on boot 66. This advantageously keeps coupling nut 64 in place by preventing it from sliding past wire assembly 69 down onto cable 40.
A second end of wire assembly 69 is secured to protective cap 68 using a second wire crimp (not numbered). Consequently, protective cap 68 is prevented from being lost or separated from preconnectorized cable 100. In this embodiment, wire assembly 69 is attached to protective cap 68 at an eyelet 68 a. Eyelet 68 a is also useful for attaching a fish-tape so that preconnectorized cable 100 can be pulled through a duct. Protective cap 68 has internal threads for engaging the external threads of coupling nut 64. Moreover, O-ring 59 provides a weatherproof seal between plug connector 50 and protective cap 68 when installed. When threadly engaged, protective cap 68 and coupling nut 64 may rotate with respect to the remainder of preconectorized cable 100, thus inhibiting torsional forces during pulling.
Many modifications and other embodiments of the present invention, within the scope of the appended claims, will become apparent to a skilled artisan. For example, the cables having other configurations such as other suitable outer designs, shapes, and/or sizes. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments may be made within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. The invention has been described with reference to cables intended for subscriber applications, but the inventive concepts of the present invention are applicable to other suitable applications as well.
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|U.S. Classification||385/102, 385/113|
|Cooperative Classification||G02B6/4429, G02B6/4422|
|Dec 22, 2004||AS||Assignment|
Owner name: CORNING CABLE SYSTEMS, LLC, NORTH CAROLINA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SEDDON, DAVID A.;HURLEY, WILLIAM C.;REEL/FRAME:016126/0952;SIGNING DATES FROM 20041220 TO 20041221
|Jan 4, 2010||FPAY||Fee payment|
Year of fee payment: 4
|Jan 6, 2014||FPAY||Fee payment|
Year of fee payment: 8